During the last year, we have extended and generalized the thermodynamic model for gelation of sickle-cell hemoglobin (HbS). The new extensions facilitate both macroscopic and microscopic characterization of the gelling process, using the results of readily performed measurements of sedimentation equilibrium and equilibrium oxygen binding. Analysis of data in the literature reveals that the tendency of HbS to gel is retained in large measure even at fractional oxygen saturations exceeding 50 percent. In collaboration with L. Fung and C. Ho of the University of Pittsburgh, we have measured and analyzed high-resolution proton NMR spectra of hemoglobin M Milwaukee. The oxygen dependence of the ferric hyperfine shifted resonances, which monitors oxygen-linked structural charge in the vicinity of the ferric beta-hemes, is inconsistent with a two-structure model of heme-heme interaction and supports the concept of direct ligand-linked interaction between subunits embodied in a sequential model.